In plastics technology, a distinction is traditionally made between three significant classes of materials, namely thermoplastics, elastomers and thermosets. In recent years, a further class of materials, the thermoplastic elastomers, has continually found new applications. Thermoplastic elastomers combine the processing properties of thermoplastics with the service properties of elastomers. The person skilled in the art is aware of various classes of these thermoplastic elastomers. A distinction can be made between two main classes, namely block copolymers (also multiblock copolymers) and elastomer alloys.
The block copolymers are composed of a hard phase and of a soft, elastic phase. The soft phases mostly form the matrix while the hard phases provide a disperse phase which acts like a crosslinking/reinforcing filler. The crosslinking regions are formed via physical bonds between the hard segments. Within their service temperatures, the block copolymers behave like crosslinked elastomers, as long as the transition temperature of the hard segments is markedly above, and that of the soft segments is markedly below, the service temperature, and the fractions in the mixture also have the correct ratio to one another.
Elastomer alloys are polymer blends which comprise thermoplastic fractions and elastomer fractions. They are produced via intensive mixing of the starting components, and crosslinking agents can be added here. If the soft phase is (to some extent) crosslinked, the term used is thermoplastic vulcanizates (TPE-V). If the soft phase has not been crosslinked, the term used is TPE-O.
The present invention relates to thermoplastic elastomers of TPE-V type. The thermoplastic used here comprises at least one polyamide.
TPE-V which have at least one polyamide as thermoplastic are known in the prior art. By way of example, EP 1 801 162 A1 relates to polyamide-EVA mixtures which have from 30 to 80% by weight of a polyamide as thermoplastic matrix, and, coupled to the thermoplastic matrix, a crosslinked disperse elastomer phase comprising from 10 to 69% by weight of an ethylene copolymer, and also from 1 to 10% by weight of a compatibilizer selected from the compounds obtained by means of grafting of α,β-ethylenically unsaturated mono- and/or dicarboxylic acids or their derivatives onto a main polymer chain provided by an ethylene copolymer, in each case based on the moulding composition. According to EP 1 801 162 A1, the intention is to provide thermoplastic moulding compositions which have good physical properties, in particular with reference to oil swelling, without any disadvantageous effect on the impact resistance, breaking stress, modulus of elasticity and tensile strain at break of the moulding composition. According to EP 1 801 162 A1, this is achieved by using from 1 to 10% by weight of a specific compatibilizer. EP 1 801 162 A1 reveals that novel thermoplastic moulding compositions are provided which have high polyamide content, namely from 30 to 80% by weight, preferably from 40 to 60% by weight, particularly preferably from 45 to 55% by weight. There is no description of the reversible elastic properties that are decisive for elastomeric materials, examples being recovery after tensile strain, or compression set.
U.S. Pat. No. 4,197,379 relates to elastoplastic compositions composed of a rubber and polyamide. The compositions have up to 50% by weight of a thermoplastic, crystalline polyamide and up to 80% by weight of a rubber, preferably of a nitrile rubber. According to U.S. Pat. No. 4,197,379 it is essential that the thermoplastic elastomers provided are essentially free from phenolic plasticizers with low molecular weight. U.S. Pat. No. 4,197,379 does not mention the use of α-olefin-vinyl acetate copolymers as elastomer component.
U.S. Pat. No. 5,270,377 relates to polyamide, mixed with a specific, to some extent crosslinked grafted polyolefin elastomer. According to U.S. Pat. No. 5,270,377 the intention is to provide compositions which have good oil resistance, mechanical strength, and heat resistance, if the elastomer component is the main component, and which have excellent impact resistance, stiffness and tensile strength if the polyamide component is the main component. U.S. Pat. No. 5,270,377 does not mention the use of α-olefin-vinyl acetate copolymers as elastomer component.
DE 44 25 944 relates to thermoplastic elastomer compositions which have from 5 to 60% by weight of a thermoplastic phase, where the thermoplastic can inter alia be a polyamide, and from 40 to 95% by weight of a crosslinked ethylene-vinyl ester copolymer or of a crosslinked grafted ethylene-vinyl ester graft copolymer. According to DE 44 25 944, the thermoplastic elastomer compositions are prepared by mixing the thermoplastic with previously crosslinked ethylene-vinyl ester polymer. No dynamic crosslinking of the elastomer component takes place during the mixing with the thermoplastic component.
It is an object of the present invention, in the light of the thermoplastic elastomers known in the prior art, to provide thermoplastic elastomers which feature a rubber-like property profile. This means that the intention is to provide thermoplastic elastomers, and compositions for the production of thermoplastic elastomers, where these have very good recovery properties, good tension set, good compression set, very good heat resistance values and solvent resistance values, and a low range of hardness (Shore hardness A). The thermoplastic elastomers are intended to be capable of processing via any desired processing techniques, such as extrusion, injection moulding, and also blow moulding.
None of the thermoplastic elastomers known hitherto can achieve a combination of properties comprising low hardness, good elastic properties, and rapid recovery together with solvent resistance and heat resistance. The thermoplastic elastomers known hitherto can either achieve good elastic properties or good heat resistance values, but with unsatisfactory solvent resistance values (in particular long-term solvent resistance values), or can achieve good solvent resistance values, but with unsatisfactory heat resistance values. Thermoplastic elastomers which have high heat resistance values and good solvent resistance values, such as TPE-A (polyetheramides), TPE-E (polyetheresters) and TPE-U (TPU, polyurethanes) are available only for applications in the (high) Shore D hardness range, in a high price segment, and have moderate elastic properties. None of the materials known hitherto in the thermoplastic elastomers (thermoplastic vulcanizates) class, TPE-V, has hitherto been capable of complying with the abovementioned requirements profile.